Duet problems with proprietary external stepper driver



  • Hi There, new to Duet (and electronics in general) and very impressed so far. My project is a 3D concrete printer. I am driving 5 axis of motion with substantial inertia and hence external stepper drivers. I have 4 of the axis successfully powering large NEMA 34's and controlled via 60V 8A external drivers connected to expansion header. The final axis involves communicating with a proprietary stepper driver I am re-purposing from another piece of equipment and powering a smaller NEMA 23. The board is clearly labeled Step, Direction, Enable, but when connections are made to the Duet, no motion results.
    I have made all connections (Dir, Stp, Enable, Gnd) and can get the motor to step by manually breaking connection in step wire, and even change direction by connecting/disconnecting direction wire. From this I assume that this proprietary board "likes it" when the low signal returns to zero voltage. It seems that the direction and step pins coming out of the Duet always read 0.5v even when signal is low.

    I have reviewed the documentation and don't see how to adjust the minimum signal voltage.

    I know the signal out from the Duet is "good" as the same wires connected to other external drivers result in motion. I have adjusted the pulse timing with no results.

    I tested the external driver just now with and Arduino and GRBL. The Arduino step pins read 0.1 volts on the low signal. Driver did not respond to this either.
    0_1533133036109_IMG_20180801_103710-03.jpeg
    Maybe this is a hardware issue where I need to somehow shift the voltage of the signal down?

    Thanks for your help!


  • administrators

    First of all, are you sure that the Duet internal drivers can't drive the smaller Nema 23 motor directly?

    The output low voltage is 0.5V because the 3.3V MCU in the Duet can't sink as much current as the 8-bit Arduinos can. I suggest you try to get it working with the Arduino first, in case low drive current turns out to be part of the problem.

    Depending on the driver, it may need either an active-high or active-low enable signal. Have you established which?



  • Thanks for quick reply! The motor is a Minebea 23KM-K709-[Illedgible]. Looks like they are rated for 3amps? This axis requires 26 watts of mechanical power and I think this motor is on the edge of that.

    I do know that the driver is active-high.

    As noted, even with the 0.1v low-state of the Arduino it still interprets a manual wire touch as a step (Motor jumps) and then does not see any subsequent steps generated by Arduino or Duet.



  • I think it's worth trying the motor directly. I run "3A" NEMA 23 motors direct from a Duet and it's been performing very well. It should provide considerably more than the necessary mechanical power.



  • @jrdm I found what I think will work for power supply and am going to try to run this off the board, as you suggest. Thanks for input.



  • @dc42 One of the things I am worried about is setting mix ratio between channels driven on the board and channels off. I see in another thread that this can be an issue. I need to synchronize the concrete extruder axis (160watt - NEMA 34) with a smaller color dispensing stepper (~20 watts - NEMA 23) Do you anticipate an issue configuring tools with mix ratios with both onboard and external drivers?(Perhaps question for separate thread)


  • administrators

    @calebc said in Duet problems with proprietary external stepper driver:

    @dc42 One of the things I am worried about is setting mix ratio between channels driven on the board and channels off. I see in another thread that this can be an issue. I need to synchronize the concrete extruder axis (160watt - NEMA 34) with a smaller color dispensing stepper (~20 watts - NEMA 23) Do you anticipate an issue configuring tools with mix ratios with both onboard and external drivers?(Perhaps question for separate thread)

    No I don't anticipate a problem doing that.


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